Amino Acids and Proteins: Characteristics and Structure

Protein Structure and Function

• The three-dimensional structure of a multisubunit protein is called a quaternary structure.
• Denaturing agents like trichloroacetic acid, phenol, and acetone can lead to protein precipitation.
• The process of refolding an unfolded (denatured) protein to restore its native structure and function is called renaturation.

Protein Composition and Formation

• Proteins consist of two separate polypeptide chains or subunits.
• About 15-20% of the body weight consists of proteins.
• Proteins are formed from amino acids.
• The amino acid sequence of a protein depends on the sequence of nucleotides in the gene that encodes it.

Amino Acid Properties

• Amino acids are divided into two main classes based on their properties: polar and nonpolar.
• Nonpolar amino acids constitute the hydrophobic core of the protein's structure.
• Polar amino acids tend to be located on the surface of a protein's structure.

Functional Groups and Bonds

• The amino and carboxyl functional groups in amino acids function as weak acids and bases.
• A peptide bond is formed by removal of the elements of water between two amino acid molecules.

Protein Structure Hierarchy

• The primary structure of a protein is the sequence of amino acids.
• The secondary structure that involves a tightly wound helical conformation of a polypeptide chain is an α-helix.
• Hydrogen bonds stabilize the structure of an α-helix in proteins.
• The secondary structure that has an extended conformation of polypeptide chains arranged into a zigzag is a β-pleated sheet.
• In a parallel β-pleated sheet, the polypeptide chains run in the same direction.
• A β-turn involves four amino acid residues and is important in compacted globular proteins.
• The tertiary structure of a protein reflects the overall 3D shape of a polypeptide chain.

Chirality and Ions

• An asymmetric carbon atom is found in amino acids with chiral centers.
• Enantiomers are compounds that are non-superposable mirror images of each other.
• Zwitterions or dipolar ions have both positive and negative charges.

Test your knowledge about the characteristics, structure, and classification of amino acids and proteins including peptide bonds, structural protein levels, 3D protein structure, and the relationship between structure and function. Explore the linear polymer formation of proteins from amino acids and their dependence on genetic information encoded in DNA.